93 D350 Cummins W/Overdrive Issues ???

OK, so, I went through several pages on this truck forum and only found one question regarding the OD transmissions but didn't really apply to my question.

The truck is a 93 D350, Cummins, 2WD with an OD trans. When the OD doesn't work, is it alright to wire the switch to stay activated ??? I've driven the truck with the switch wired/bypassed and it seems to be alright that way ??? Before we wired it direct to stay on ... the trans would buck & kick like it couldn't see the signal to go in overdrive ?? I've occasionally seen posts regarding the OD on this era of truck but never paid any attention to the details because I've mostly had stick trucks ...

Thx in advance ...

On my 92 I got tired of changing out the od switch ($100 if I remember right and didn’t last long) so I put an on off switch on the gear selector arm, I’d cut it off once truck gets back to a stop turn back on once it was in third. Never any issues with shifting

[Sort of what we did to see if it would drive out like that but went through the button on the dash to stay on all the time when driving and no problems. My concern is for long-term driving on trips of 500 - 1000 miles and so ??

quote=cudaman1969]On my 92 I got tired of changing out the od switch ($100 if I remember right and didn’t last long) so I put an on off switch on the gear selector arm, I’d cut it off once truck gets back to a stop turn back on once it was in third. Never any issues with shifting [/quote]

The factory dash switch is to turn off OD. It sends a signal to the computer to lock out OD.

You can indeed wire the solenoid for manual control. It won't hurt the transmission.

OK, thx ... That is my main concern. As long as we keep the switch on/wired to bypass and operating as an on/off switch, t seems to be alright.

All the switch on the dash does is disconnect the ground(from the pcm when od is engaged) to keep it out of od. If you plan to use a switch just to supply a ground(not from the pcm) for the od to engage is another story. You will engage the od with the switch regardless of what gear you are in. Pcm engages and disengages the od as needed.

I ran it that way 7 years till it was sold became second nature like shifting a stick.

It certainly won't hurt it, but it is a PITA. You have to turn it off if you want the trans to downshift and if you leave it on when coming to a stop it stays locked up, shudders and shakes until it shifts to first. 99% of the time O/D shifting hunting or inoperative conditions are caused by the TPS. Could also be a CKPS or a VSS. If it was a crank sensor though the A/C compressor won't kick on. If it's a VSS then the cruise won't work. I know the TPS isn't cheap but it isn't super expensive either. Geno's Garage carries them.

I don't think OD engagement will cause a shake, TCC will. Iirc the internal plumbing prevents OD engagement in first and second, the OD solenoid doesn't get pressurized oil until the transmission reaches 3rd gear. This seems like it effectively keeps the transmission a 3 speed but with a really wide spread between 2nd and OD as it basically would skip 3rd altogether.

You are correct, mine has lockup and I was thinking like that.